The use of printed circuits is widespread in the electrical and electronics industries. Both rigid and flexible materials as well as combinations of the two are used. A distinction is drawn between soldering bathproof systems and those not suitable for soldering baths.
In both, the printed circuit is a non-conductive substrate base and conductive materials in strips on the substrate or base forming an electrical circuit. Frequently glass fiber reinforced epoxy resin sheets, polyimide or polyester films are used as base materials. The generation of the strip conductor image on the substrate, which is originally completely covered with copper, takes place in an etching process. After the substrate layered with a photo-sensitive lacquer has been illuminated with the strip conductor image to be generated, the copper-covered substrate is etched. The copper layering consists of electrolyte copper at a thickness of for example 0.035 mm, attached to the substrate with a heat- and chemical-resistant adhesive. Therefore, for the manufacture of a printed circuit, in addition to the preparation of the photographic pattern, a slow, multi-stage etching process is necessary which must be repeated on each individual piece and must be very accurately controlled in relation to temperatures and concentrations of the agents. Inspite of this, the danger of etching errors, such as under-etching or similar, exists.
For this reason there have been numerous attempts to circumvent the etching process. Thus it was suggested that the strip conductors be manufactured by printing with a lacquer filled with an electrically conducting material. This process is preferred in the manufacture of the base films for membrane switches.
A further process is the transfer of the strip conductors by hot embossing. In this process, the strip conductors are represented raised on an embossing stamp. A synthetic film, for example polyester film, is layered by means of an adhesion imparter (also termed a separating layer) with a special film, whose sealing temperature lies above the melting temperature of the abovementioned separationlayer. With this process strip conductors can be applied to suitable thermoplastic or nonthermoplastic substrates of any shape. In particular, endless printing with roller-shaped embossing tools is possible for large number of pieces.
The object of the present invention was to circumvent certain disadvantages of the above-mentioned embossing process. These disadvantages are in particular;
1. The minimum breadth of the strip conductors must not be less than 0.2 mm.
2. The minimum separation between neighbouring strip conductors must not be less than 0.5 mm.
3. For the generation of high quality printed circuits the maintenance of very exact temperatures of the embossing tool is required, to which end expensive controls are necessary in particular with larger embossing tools.
The present invention avoids the aforementioned disadvantages. It was surprisingly shown that it was possible to fall significantly below the above-mentioned minimum breadth and separations, and thereby significantly extend the possible application of the printed circuits manufactured according to the invention in relation to more densely fitted circuits.